[Click to enlarge] Introduction: The car turns over but won't start in hot weather is a symptom of a main relay going bad. This is the result of the poor solder application from the factory. As a consequence, raise areas on the joint indicate a "dry" joint which can lead to an open circuit. This is caused by expansion, contraction and dirt in the joint area and has resulted in an unacceptably high resistance. When the terminals expand, contract and vibrate, it is likely that a layer of hard oxide has built up inside the joint. The layers are to be removed by desoldering. The steps to desoldering can be found on this page.

For this repair project you will need these:
main relay or [90-93 Acura Legend Main relay] or Acura Honda Main relay

A bare-bone main relay, Where can I find the MainRelay?

a 15-30 watt soldering iron or 600F - 700F

a Rosin core solder

a solder wick or

a De-soldering pump

Start by carefully prying the main relay:

Clip----->main relay Stick a flat small flat screw driver in between.

Separation Steps: What to look for:
Picture of separation procedure Picture of where to solder
Fig. 12 click to enlarge

1. Stick a small flat head screw driver in between the wall flap (a clip) and the relay base.
2. Do not go in too deep. Pry it open just slightly.
3. While holding it still, use the same screw driver, pry the other side.
4. While holding it still (and cleared of the locking edge) pull the relay straight out, or forward.
5. Installation is reverse of the procedure (Note: The main relay will only go in one way into the housing.)

Warning: Do not stick the screw driver too deep inside. You may damage the relay's mechanical or electrical parts.

How to solder correctly

The image above and below shows several good and bad examples. More soldering examples (external link.)

TIPS: Image of how to solder main relay correctly. Image of how to solder main relay correctly.
A joint with insufficient solder is a joint failure waiting to happen, as do dry joints.

CAUTION:

Try not to heat the joint too long, because the copper traces on the circuit board may lift.

Health warning:

Do not over expose your lungs or eyes to the fumes. Wash hands with soap and water after handling the PCB's and leads.

Quick Step 1: Desolder the faulty relay terminals
(click on this image or fig. 12 above.)
Picture of where to solder

Desolder using pump [Heat the solder, position pump vertical to the terminal. Remove the solder gun and suck the melted solder.] Or desolder using a wick [Heat the solder, press the wick down on the
solder with the gun then snip out the used wick and repeat.]

Step 2: Heat the terminal and the copper trace with the soldering tip while applying rosin core solder to terminal. [Heat the terminal then apply solder. Position the relay on its side to stop solder from running out the bottom.]

If you do have a joint which looks in need of rework don't be tempted to just reapply the iron. This is unlikely to succeed as the solder in place will have no flux in it, so the flow across the joint will be worse than when it was first made. Better to remove the solder, using a desoldering pump or copper braid, and make the joint again. The flux's job is to strip away all of the grease from the surfaces to be soldered, thus ensuring that the solder will flow properly. A concave should be formed with an angle of 40 and 70° from the horizontal.

Step 4: Install onto the vehicle in a lower, practical location, easily accessible in the future. Your work is done.
See all locations >>

Further explanations: When the relay terminal cannot dissipate heat, the solder on the joint weakens, a "dry" joint is formed resulting in an unacceptably high resistance. The joint begins to heat then subject to vibrations, eventually oxides would form and eventually lead to an open circuit once the motor is shut off. Once cooled the terminal contracts downward and complete the circuit. The dry solder joints could have been easily eliminated if the solder quality is consistent, a concave should be formed with an angle of 40 and 70° from the horizontal and shiny. Four terminals and maybe more on the main relay are known behave this way.

Should I remove the old solder?

Yes. The old solder is of poor quality and damaged. Black areas on the joint indicate a "dry" joint. This is caused by dirt in the joint area and will result in an unacceptably high resistance.

What happens if I just reheat or add additional solder to the joints?

The joint area will result in an unacceptably high resistance. Your symptom may return much earlier than a brand new main relay. The car may stall in traffic and won't start.